


Kamen Rider Ryuki: Episode Build

by Rainbowfootsteps



Category: Kamen Rider Build, Kamen Rider Ryuki
Genre: Alternate Universe, Canon Compliant, Canon Timeline, Crossover, Gen, M/M, kind of, you know how it is with ryuki
Language: English
Status: In-Progress
Published: 2021-02-25
Updated: 2021-03-04
Packaged: 2021-03-16 02:42:51
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 4
Words: 6,404
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29693820
Author URL: https://archiveofourown.org/users/Rainbowfootsteps/pseuds/Rainbowfootsteps
Summary: Shiro Kanzaki tries to remove Shinji from the rider battle, but in doing so, creates a rip in space-time that transports Sento and Banjou to the world of Ryuki. This is my playplace and I do what I want
Relationships: Akiyama Ren/Kido Shinji, Banjou Ryuuga/Kiryuu Sento, Kitaoka Shuuichi/Yura Gorou
Comments: 2
Kudos: 7





	1. In Another World With My Boyfriend!?

**Author's Note:**

> Warning: Allusion to a canonical suicide in this chapter  
> This Ryuki timeline happens directly after Ryuki: Episode Final so there are some light spoilers for that, as well as obviously spoilers for both Build and Ryuki. Other riders might turn up later idk so just Watch Out

This was his fifteenth time. Sixteenth? He had lost count. It was hard to keep track of time when time itself was malleable, able to be reverted and toyed with as much as necessary. Such was the blessing of Odin. Shiro Kanzaki ran his finger down the edge of Survive Mugen, feeling the card dig into his skin. Every time he restarted the rider battle, he started in the same place; in their childhood home, back against the wall, gazing into Mugen’s golden eye. 

The last loop had ended badly. Lucid, garish memories of blood dripping down Yui’s wrist were blazed into his mind. He remembered the anguished howls that had escaped him. 

He wouldn’t let that happen again. 

That bastard. Every single time, Shinji found the Ryuki deck. Every single time, he ruined the battle with his insipid meddling. No amount of threats or suggestions could make him fight for a wish. Shiro let Mugen fall from his fingers, and curled his hand into a fist. Not this time. If he couldn’t convince Shinji to fight, then he would break the rules. 

“Odin. This time, only twelve riders will fight.”

* * *

Something was wrong with the motorbike. Each time Sento fiddled with the engine, the machine made a concerning squealing noise, not unlike a wounded hamster. Surely a physicist could wrestle a simple engine into submission, right?

“I got you a coffee.” Banjou’s voice floated from the other side of the garage. Sento looked up just in time to catch the can Banjou threw to him. 

“Only a small one? Cheapskate,” Sento teased. Banjou snorted, paused to knock back his own coffee in one gulp, then swung his leg over the motorbike’s seat.

“Stop moving the bike, idiot.” Sento complained. He smacked Banjou’s leg, and Banjou kicked him in return. With a sigh, Sento leant back. He carefully opened his coffee can and took a sip. 

“It’s pretty nice that nobody knows who we are anymore,” Banjou said offhandedly. He leant his head on the motorbike’s handlebar. “I could go to a vending machine and not get any weird looks. It was pretty stressful being a criminal at large.”

He slid off the motorbike and sat on the floor next to Sento. “I’m glad you still know who I am, though.”

“You are?”

“I know, it surprises me too.”

Sento couldn’t hide his smile. He poked Banjou’s shoulder, then kissed him. Even in a different world where they didn’t quite fit, they were still a Best Match.

Crack.

Sento drew away from Banjou with wide, confused eyes.

“Did you hear that?”

“Hear what?”

 _Crack. Scratch…_ The sound was like ringing metal, and glass slowly cracking. Banjou suddenly stiffened and looked around them. They quickly scrambled to their feet, back-to-back. The sound grew, pulsing, almost animalistic. 

_Crash!_

“Ren… Ren, do the dishes… Uhn…” Shinji’s eyes slowly blinked open, struggling to see into the darkness around him. As his wits returned to him, he slowly became aware of several curious facts. One, he wasn’t in bed. Two, his body felt sore. Three, he was somewhere dark and cold. He mulled over these for a while, then struggled into a sitting position. He glanced around him. 

His blood ran cold.

He was in Yui’s childhood home. White sheets lay over the few pieces of furniture in the room, and newspaper was taped over every window. The heavy wooden door was closed, and someone was lying on the floor next to him. Wait, what?

He shuffled closer to the unconscious man beside him. The man had black hair and a youthful, slightly impish face, and mismatched shoes. Could this be another rider?

“Um, hello? Are you okay?” Shinji gently pushed the man’s shoulder. The man’s eyes fluttered open almost immediately. Shinji yelped and shuffled backwards.

“Ah, sorry..!” Shinji winced as the man stared at him. “I’m Shinji Kido. Are you a rider?”

“A rider… A rider?” the man echoed. His eyes narrowed. “How do you know that?” 

“It’s okay, I’m a rider too.” Shinji put his hand into his pocket - but to his horror, didn’t feel the cool metal of his advent deck. He frantically checked each pocket in turn, much to the bemusement of his new companion.

“Seriously..? But I’m a Rider, really!” He insisted. “You’re one too, right? That’s why someone brought us here.”

“I am a rider, but… where is here?” The man asked. He got to his feet and checked the door - locked. 

“Shiro Kanzaki’s house. The man who gave you your advent deck,” Shinji replied. Sento stared at him like he had two heads. 

“I don’t have an ‘advent deck’, whatever that is. Who are you, and what’s going on?”

* * *

When Banjou came to, he was on the ground with blood in his mouth. He coughed, blinked, and struggled to his feet. He was on an empty street, and the sound of metal and glass was still loud in his ears. His head hurt so much it was hard to focus, but he tried to remember how he’d ended up here.

Before he could look around properly, the glass sound suddenly ended. Right before his eyes, he watched in amazement as a figure stepped out of a rippling glass window. The figure was clad in dark blue and grey, styled almost like a medieval knight. Around his waist was a belt, from which he withdrew a blue rectangle. Like shattered glass the armour fell away, leaving a man with wild black hair and a foul look on his face.

Banjou stared dumbly as the man stormed up to him and gripped his collar tightly.

“What did you do with Shinji, you bastard?” The man snarled. His cheekbones were almost as sharp as his tongue, and his fashion sense reminded Banjou of the Matrix. Banjou let out an unintelligible squeak, then tried to speak.

“I dunno who Shinji is, asshole! Let go of me!” He pulled at the man’s hand. The look on the man’s face darkened, but he eventually let go of Banjou.

“You’re a rider, aren’t you. If you think you can blackmail me, it won’t work. So how about you tell me where Shinji is before I rip you limb from limb.” He growled. 

“I told you, I don’t know who Shinji is! But… How did you know I was a rider?” He eyed the other man uncertainly.

“Don’t play games with me.” The man snapped. He seemed ready to punch Banjou in the face, but a yell rang out through the street.

“Ren! Stop it!” Banjou craned his neck to see who was talking. From the corner of his eye he saw a young woman with short brown hair and a concerned look on her face.

“Yui…” Ren gave Banjou one last glare, then turned away. Yui ran to Banjou, then looked him up and down.

“Please don’t fight Ren..!”

“Um, okay, I won’t.” Banjou assured her. “But, uh, sorry, I’m super lost right now. I think I got teleported or something. Are you a rider too?” 

Yui and Ren shared an indecipherable look. Then she turned back to Banjou.

“Something weird is going on. How about we go to my aunt’s cafe, and we can sort this out.” She suggested. Banjou nodded weakly. Kamen Riders coming out of the woodwork, some guy called Shinji… What the fuck was going on?

* * *

“Thanks for, uh, stopping your friend from killing me.” Banjou accepted the cup of tea Yui handed to him, and tried to ignore the scowl Ren was burning into him. The cafe the two had brought him to was reminiscent of cafe Nascita. Off-white walls and metal fence aside, it made him yearn for the cafe he knew so well. He looked down at the black tea in his hands, and thought about the coffee can in Sento’s hands.

Yui sat across from him and exhaled quietly. “I think you should try and tell us who you are.”

Banjou nodded. “I guess it’s okay to tell you guys. I’m a kamen rider like Neo over here-” he fished his Dragon Fullbottle out of his pocket and held it up for Yui to see- “ but where I’m from people don’t walk out of windows. And me n’ Sento, we’re pretty much the only kamen riders…”

“Sento?” Yui echoed.

“He’s my boyfriend. He’s a kamen rider too, and he’d probably know what’s going on right now if he was here,” Banjou replied. He couldn’t help but grin when telling people about Sento, pride in his boyfriend overtaking his concerns. “He’s like, really smart, and kind of a dick. He’s the one who made my Fullbottle adaptor.”

Ren walked beside Banjou, and placed something on the table. It was the same blue rectangle Banjou had seen him pull from his belt earlier - now he could see a golden symbol emblazoned in the middle, and an indent where the tops of cards could be seen.

“The only way to become a kamen rider is using an advent deck,” Ren told him coolly. “And there are only thirteen riders.”

“Well, maybe here that’s true, but not where I’m from,” Banjou grumbled. “Anyway, how did you walk out of a window?”

“That’s the Mirror World,” Yui interjected. “Monsters in the Mirror World prey on humans in our world. Every kamen rider has a contract with a monster… But I suppose that’s not true for you.”

“Yeah, um, okay. No, I don’t have a pet monster,” Banjou replied with a nervous chuckle. From the glare Ren gave him, this was clearly the wrong answer.

“You’re lucky I’m not letting Darkwing eat your soul right now,” he sniped. 

“Don’t threaten me, asshole.” Banjou stood up from his seat and drew himself to full height. Unfortunately he was a hair shorter than Ren, and the taller man was much better at looking intimidating.

“Stop it, you two!” Yui grabbed Ren’s shoulder, and dragged him back a step. “We should focus on finding Shinji.”

“Yeah, about that. Who’s Shinji?”


	2. Golden Feathers

“So, just to check I’ve got this right: you’re a kamen rider, you fight other kamen riders to get a wish, and this Shiro guy is the one who gave you all your advent decks.”

“Yeah! But I don’t really have a wish. I just want the fighting to end…” Shinji lamented. He and Sento had cast aside the sheets covering every table and chair, and pulled the heavy wooden furniture together to make a crude sitting area. Shinji perched on a chair with his arms hugging his legs, while Sento stood behind a chair, one hand fiddling with his hair. 

“This is some kind of alternate universe. Shiro has the power to travel through space and create the advent decks, so a tear in space-time isn’t inconceivable… But why would he bring me here?” Sento began to pace back and forth, his mind swirling with questions. There was a reason for everything - he just had to find it.

_Scratch… Ring…_

Shinji jumped to his feet. 

“I’ve heard this before, just before I was sent here.” Sento said quietly. Shinji instinctively reached for his advent deck, and grimaced when he remembered he didn’t have it.

“That’s mirror noise. Something is going on in the mirror world,” He warned.

“Curious.”

The voice came from behind them. Shinji felt a shiver run down his spine.

Shiro Kanzaki stood before the door, a card hanging listlessly between two fingers. He watched the other two men from beneath his dark hair, a grim smile on his lips. 

“Kanzaki…” Shinji’s hand balled into a fist. “If you’re here to tell me to fight, I won’t.”

Shiro didn’t move. After a weighty pause, he slipped the card into his pocket.

When he finally spoke, it was with a wry smile. “You don’t need to fight anymore, Kido. I won’t allow you to ruin things this time. This time, I’m removing you from the battle myself.”

“I don’t think so,” Sento replied calmly. He pulled two Fullbottles from his jacket - rabbit and tank, the two he never went without. Pushing the Build Driver to his waist and slotting in the Fullbottles was muscle memory, and he watched closely for a reaction from Kanzaki as he began his transformation.

“Henshin!”

Shinji scrambled out of the way just in time. Sento’s transformation nearly filled the room, pillars of steam shooting off as he became Kamen Rider Build.

“You’re not laying a finger on Shinji.” Sento announced. Shiro seemed to judge him for a moment. 

“Unexpected, but… You won’t get in my way.” Shiro replied. To Sento’s surprise, a cloud of golden feathers seemed to appear from nowhere, enveloping Shiro in a glimmering cloud. When they dispersed, a Kamen Rider remained.

“Odin..!” Shinji squeaked. Sento appraised his opposition. Odin was reminiscent of a phoenix, with great feathered pauldrons and a bronze staff adorned with wings. Was this still Shiro, or someone different? In this world, things seemed to often be different than they appeared. He stood still as stone; it seemed Shiro was waiting for Sento to make the first move. Fine, he didn’t mind.

Sento drew his fist back, and thrust it at Odin’s head. Crash! His fist connected with the wooden door. Somehow behind him, Odin kicked him between the shoulderblades, slamming him into the door. Sento twisted around to throw another punch, but again, Odin was gone before the hit landed. This time Odin slammed his staff into Sento’s side and sent him sprawling to the floor.

“You are beneath me.” Odin spoke in deep, heavy tones. “Only the one who wins the rider battle may fight against Odin.”

Sento winced at the pain, but got back on his feet. “I don’t care.” He launched himself at Odin once again - was cast aside again. This time Odin ignored him and marched towards Shinji. He gripped Shinji’s shirt, staff pressed against his chest. 

He pulled back his arm

and

Faltered. Shinji gasped as Odin suddenly threw him aside. Odin himself seemed to suddenly be fighting against himself. 

“No… Dammit… The timeline… Already weakened…” Odin muttered to himself. Eventually he walked to Sento, ripped his Build Driver from him, and was gone as quickly as he had appeared.

“Ungh…” Sento could taste blood. His Build Driver was gone. Odin was gone. And now he had even more unanswered questions.

* * *

Shuichi was in a good mood today. Another legal case had gone his way, and Goro’s gyoza had improved remarkably. So it was with a sense of self satisfaction that he found himself taking a walk around town. The shopping street was pleasantly quiet at this late hour. Even his illness was behaving itself today; the ache he always felt deep in his bones was barely noticeable. 

Of course, it was just his luck that such a good day would be ruined by seeing Ren Akiyama. Shuichi groaned internally when he saw the tall man and his insufferable leather trench coat. He was about to turn down a side street to avoid a confrontation with him when he noticed an odd man walking next to Ren.

What really caught his eye about the man was his strange, out of place dress. A plaid shirt was tied around his waist, and he wore a black and white varsity jacket. If this was the new fashion trend, Shuichi was glad he was too old for it.

He leant against the wall of a shop and waited for Ren to notice him. As he watched the two, his mind began to wander. Perhaps he should make dinner tonight. Goro was overworking himself recently, he deserved it.

“Kitaoka.” Ren’s contemptuous voice returned him to reality. Shuichi smiled thinly, giving a curt wave to the other rider. 

“It’s not like you to have friends, Akiyama,” Shuichi purred. “Have you decided to change your ways?”

“Eh? You know this guy?” The mysterious man put his hands on his hips and looked Shuichi up and down. “Don’t tell me he’s a rider too.”

Shuichi immediately perked up. Now this was interesting. He fished a business card from his pocket and passed it to the man with a sly grin.

“Shuichi Kitaoka, master lawyer. Pleased to make your acquaintance.”

The man looked at him suspiciously. “Uh… Banjou Ryuga. Kinda lost at the moment. So you and Ren like, fight and stuff?”

Shuichi generally tried to keep his emotions under control, but he couldn’t help being visibly taken aback. “You’re a rider, aren’t you? Don’t tell me you’re an ignorant fool like Shinji.”

Banjou bristled. “I don’t mind fighting you if that’s what you want, you prick.”

Ren put a hand on Banjou’s shoulder and forcibly dragged him away from Shuichi. “Get yourself under control. We’re not here to fight.”

“How odd to hear that from you,” Shuichi observed. “Normally that’s Shinji’s line… And normally he’s with you.” His eyes narrowed. “Something’s going on.”

Ren’s scowl deepened. “We don’t need your help.”

_Creak… Ring…_

Shuichi took a step back. Now, of all times? He and Ren both reached for their advent decks, but Banjou just seemed confused. Had he only just received a deck?

“What’s going on?” Banjou clutched his head in one hand. 

“That’s mirror noise. A monster is nearby. Did Shiro not tell you anything?” Shuichi asked incredulously. 

“Shiro…?” Banjou stared at him blankly. Ugh, he didn’t have time for this. Shuichi ran to the nearest glass - a bus station’s reflective wall, the other side plastered with posters and stickers.

“Henshin!”

He and Ren transformed together. It was always slightly strange to suddenly feel the weight of Zolda’s armour on his body, but it always filled Shuichi with a sense of strength he craved. He rolled his shoulders, relishing the feeling, then turned to look at Banjou. The man bit his lip, glanced down at his hand, then looked back up at Shuichi and Ren. 

“Okay, I dunno what’s going on, but I’ll help if I can.” He said. From his pocket he pulled out a small cubelike contraption.

“Henshin!”

Shuichi had never seen anything like it. A mass of pipes appeared from nowhere, swarming around Banjou before slamming into him in a burst of flames. When they receded Banjou was clad in rider armour - but it was nothing like the armour Shuichi had seen on the other riders. Flames snaked up his arms and shoulders, the eyes of the helmet jagged and blue like ice. And he hadn’t used an advent deck to transform. Fascinating. 

But he didn’t have time to just stand and stare. The mirror noise was growing, and he could hear the faint growls of a nearby mirror monster. He faced the mirror and stepped inside.

The mirror world was always so remarkably cold. There was never even a breeze - instead everything felt frozen. Shuichi hated it. He glanced to his left and saw Ren step out of his Rideshooter. 

“Ahh!” The glass he had just driven out of began to ripple, then contort as Banjou stumbled out of it. He immediately bent over forwards, gasping for air.

“What- the fuck- was that?” He stammered, looking up at the sterile world he now found himself in.

“You’re in the mirror world now.” Shuichi replied. “So don’t take off your armour, or you’re dead. Although, you’re clearly not using an advent deck, so you might just die anyway.”

“Wonderful.” Banjou muttered. An inhuman screech distracted the three from their conversation. From across the street, a monster was watching them.

It took a single bound for the beast to reach them. It was a disgusting creature - blue and squid-like, with writhing tentacles protruding from its malformed head. Shuichi cocked his gun and slipped a card in.

_‘Guard vent.’_

Shuichi gripped Magnugiga’s shield just in time to deflect a blow from the creature, responding in turn with a barrage of bullets. Ren charged at the beast, his sword plunging into its flesh. The monster howled and directed its hatred at Ren. Shuichi used this opportunity to intently watch Banjou. Clearly he couldn’t use any cards, so what would he do?

The answer, it seemed, was the direct approach. Banjou slammed his fist into the creature, sending it careening backwards. He and Ren made short work of the beast, pushing it back further and further. It seemed they had completely forgotten about Shuichi. No matter. He smiled to himself, and slowly opened his gun’s magazine. 

_‘Final Vent.’_ He watched with silent satisfaction as Ren plunged his sword into the monster, and Darkwing snatched away its soul. Magnugiga rose to stand before him, and Shuichi carefully locked his gun into place. He could feel the hot thrum of Magnugiga charging. He didn’t mind waiting. He watched Ren and Banjou step back from the eviscerated monster, look at each other.

Now.

He pulled the trigger.

An explosion of bullets and missiles rocketed out of Magnugiga, choking the air with smoke. Shuichi had to brace himself to avoid getting flung backwards, but it was worth it. The missiles connected with an almighty roar.


	3. Convergence

Sento was pretty sure he could pick the lock. Not entirely sure, but maybe… 74% sure. He delicately slotted the bent paperclip into the door’s lock.

“Hey, Sento…” Shinji rested against the wall beside him. “You haven’t told me anything about the world you’re from.”

“Not much to tell,” Sento replied. “There’s certainly no rider battle. Kamen riders work together, for love-and-peace!”

“Sounds nice… I wish I could get everyone to work together. But I can’t even convince Ren.”

“Is he your partner?”

“We’re friends! Well… I think he’s my friend. If you asked him, he’d probably say he doesn’t know me.”

“Hah, that sounds like Banjou. I wonder if he got transported here too…”

“Banjou? Is he a rider too?”

“Yeah, he’s my boyfriend. He’s about as smart as a monkey,” Sento said with a smile, “but he’s my idiot.”

Shinji nodded slowly. He couldn’t help but feel useless, sitting around while his newfound friend wrestled with the lock. Each pocket on his person he’d checked in turn, only to find out his phone’s battery was dead.

“Ugh, this sucks..!” Shinji moaned. “At least it’s saturday, I think. My boss would kill me if I was late to work again.”

“Office job?” Sento asked, his attention still focused on the lock.

“I’m a journalist!” Shinji replied proudly. “If you were from around here, you’d have totally heard of me.”

“I’m sure.”

“What do you do, anyway?”

Sento moved his weight backwards, resting on his heels. He looked at the warped paper clip in his hand, then at Shinji. “A long time ago, I was a physicist. But… It’s complicated.”

“Man, you’re way smarter than me…” Shinji murmured. Sento smiled, and returned to the lock.

_Scratch. Scratch._

_Click._

The door swung open. 

“Ah! You’re the best!” Shinji shot to his feet and grabbed Sento in a hug, filled with delight. Sento chuckled and hugged him back. 

“Come on, let’s get out of here,” Sento said with a smile. 

It was clear that this house was long abandoned. The door opened into a silent hall, undisturbed dust lying like a carpet on the floor. But how was it unmoved, if Shiro had been through here? Sento’s eyebrows furrowed. 

Downstairs was more of the same. White sheets standing like ghosts of a time long past amongst pale brown wood. Two large front doors stood directly across from the staircase. Shinji gave one an experimental tug. It was locked, but had some give. He inhaled sharply, lifted his foot up, and kicked.

_Bang!_

The door flew open. Shinji grinned at Sento, who raised his eyebrows.

“What now?” He asked.

“Now we’ve gotta find Ren and tell him everything.”

* * *

“What the hell is wrong with you?!” 

Blood dripped from Banjou’s cheek, his knee, his hand. His hair stuck to his scalp from sweat. It was all he could do to stagger towards the calm suited man, who watched him with smug ambivalence. Banjou reached up to grab Shuichi’s tie, but he was easily swatted away. His legs buckled, and he crumpled to the ground.

“What are you not understanding about the battle?” Shuichi replied calmly. “You agreed to this when you joined.”

“He’s not part of the rider battle.” Ren yelled. His knuckles were raw and red, but he had avoided the worst of Magnugiga’s assault. He stormed towards Shuichi with a black scowl on his face. “He doesn’t have an advent deck. He’s not supposed to be here. I don’t care if you kill him, but don’t you think you’d rather know why he’s even here?”

Shuichi examined a fingernail, feigning flippancy. “Well, I certainly won’t waste time on him. But… Where’s Kido? Normally he follows you like a lost puppy.”

“Before you tried to fucking kill us, we were looking for him.” Banjou grumbled, rolling his shoulder and wincing at his sore muscles. 

“Well, good luck.” Shuichi gave them a cold smile, tucked his advent deck into his suit pocket, and turned to leave. Banjou watched him go, then glanced at Ren.

“What’s his problem?” He moaned. “We took care of that monster for him and everything!”

“That’s now how the rider battle works,” Ren replied sharply. “Get up. It’s getting late; we’ll keep looking tomorrow.”

* * *

The building was long abandoned. Rubble lay strewn across the ground, interlaced with choked weeds. Thin reeds of moonlight filtered through the broken roof, casting long lines of light through the dust-filled air. Flames licked upwards from a blazing barrel. The fire made orange light dance across Asakura’s face, illuminating his sly gaze. In front of him, left on a thick chunk of rubble, was a single card. 

He knew Shiro was there with him before he could see him. 

“Asakura Takeshi. Use the survive card. Defeat the other riders.”

Asakura ran his tongue over his teeth.

“Kill Shinji Kido.” Shiro stood by the fire, watching the flames intently. He glanced at Asakura. In Shiro’s hand was Shinji’s advent deck. Asakura grinned.

“I won’t fight someone who can’t fight back. Where’s the fun in that?”

Shiro’s jaw tensed. Then he tossed the advent deck to Asakura - he caught it and gazed at it, watching the light catch its metallic surface. 

“Then take this too.” Shiro placed a strange, black rectangle on the ground. Adorned with a large red crank, two bottles - one red, one blue - were slotted into it. “Your new prey will need it if you want to kill him too.”

“I don’t do what you tell me to.” Asakura replied, letting Shinji’s advent deck fall to the ground. It clattered aside, landing near the odd black device.

“I know. But if you want your wish to come true, you’ll kill Shinji Kido.” Shiro replied. Asakura laughed. If only Shiro knew. If only he knew what he felt, every moment. The beating drum, the euphoric rush, the bottomless craving for violence that propelled his every action. Asakura was patient. He could wait. He could wait as long as it took to get the chance to rip Shiro’s head from his body, to watch the life bleed from his eyes. He could wait.

* * *

By the time Shinji and Sento arrived at the cafe, the moon had risen. They’d spent the walk talking - more accurately, with Sento grilling Shinji for information - and by the time the cafe came into view, Shinji was thoroughly exhausted. He pushed the door open, made a beeline to the nearest chair, and collapsed in it.

“Maaan, I’m tired..!” He flopped his head on the table. Sento glanced around the cafe. 

“Is Ren upstairs?”

“Ehhh… Probably…”

Sento need not have asked. Before he could explore, the sound of footsteps floated from the staircase.

“Kido!” A tall, darkly dressed man emerged from the staircase. His hair was impossibly pointed, reminding Sento of his hedgehog fullbottle. 

“Ah, Ren!” Shinji sat up, giving Ren a cheesy grin. “I’m home!”

“Where the hell have you been?” Ren demanded. “And who are you?”

“Sento Kiryuu. Physicist, genius, kamen rider. I’m sure this is a lot to take in, but Shinji and I were attacked by Shiro Kanzaki.”

Ren stared at him, then at Shinji. “What?”

“I dunno either…” Shinji mumbled. “I was just… I dunno what I was doing, but then I was asleep and I woke up in Shiro’s house. And Sento was there, and then Shiro was gonna attack me but then he didn’t, and he took my advent deck! Dragreder is gonna be so mad!”

Ren’s lip curled. “That’s what you’re worried about right now? We’ve been looking for you for hours!”

“Maybe we should talk about this in the morning,” Sento suggested. “Your friend Kido and I have been through a lot today.”

Ren still looked annoyed, but he eventually relented. “Fine. And you’re Sento. Your friend Banjou is upstairs.”

Sento’s eyes widened. “Banjou is here too?” He hurried past Ren and up the stairs. The cafe’s upstairs was small, and it didn’t take long for him to pinpoint the source of the soft snoring he knew so well. 

The small guest room was comfortably small, with a bed for two in the middle of the back wall. On top of the duvet, with his shoes still on, Banjou had fallen asleep, his dragon Fullbottle still in his hand. 

“Hey, idiot.” Sento poked his arm. Looking closer, he could see bruises on Banjou’s face and arms. “Banjou… Wake up already.”

“Eh…” Banjou’s eyes opened sluggishly. He blinked and looked at Sento. 

“EH? Sento!” He sat bolt upright, making Sento laugh.

“Calm down, dude.”

“Calm down? Do you have any idea what’s happened today?”

“Uh, not really, no. I was hoping you’d say something like ‘I’m so glad you’re safe’ or something.”

“Geez, man. I thought that went without saying.”

Sento snorted, and shuffled onto the bed next to Banjou. The two lay back down again, too tired to bother getting into bed properly. Banjou gently put his arm behind Sento’s shoulders, pulling him in close.

“I was worried about you, man.” He mumbled. Sento’s smell was comfortingly familiar; his own brand of shampoo that he never let Banjou use… It reminded him of home. “Like, what if I was here, wherever here is, and you weren’t, you know?”

“Well, I’m wherever here is, so stop worrying.” Sento replied. He was trying to act cool about it, but Banjou could tell how he was really feeling. His hands held tightly to Banjou’s jacket, keeping him close.

**Notes for the Chapter:**

> Ouja survive >:)


	4. Anguiform

**Notes for the Chapter:**

> graphic descriptions of violence ahead

“There are two most likely explanations for what’s going on.” 

Sento paced back and forth on the cafe floor. His eyes sparkled with deductive delight, one hand permanently in his hair ruffling and smoothing a stray lock of hair. Shinji, Banjou, Ren and Yui watched him with a mixture of curiousity and skepticism.

“It’s currently… 2002. We may be in the same world, just in a different time. But there’s no record of any of this where we live - no news stories, nothing. Something could happen that wipes out any memory of these events, but I don’t think that’s the case. I searched hospital records on Yui’s computer, and there’s no birth records for Katsuragi Takumi.”

“Why didn’t you search for yourself?” Shinji asked. Sento smiled wryly. 

“Oh, I did.” 

Shinji frowned and crossed his arms. “Man, you’re so confusing…”

“Anyway, I’m fairly certain this is an alternate reality, fully separate from our own. Shiro Kanzaki somehow transported us here, and before or during this, also kidnapped Shinji with the intent to kill him.”

“Why would he bring you two here?” Ren challenged. “You’re not part of the Rider Battle.”

“An excellent question,” Sento replied. “I don’t think he did it on purpose. Messing with the flow of time gets messy, believe me. It’s likely we were a byproduct of Shiro causing some kind of large disturbance to the flow of time in this reality.”

Until now, Yui had been silent. Now, she looked away from Sento, her expression pained.

“Shiro… I wish he would just come home. I don’t understand him at all…”

“We’ll do everything we can to work this out,” Banjou promised. “I don’t really get anything Sento said either, but I promise we’re gonna work all this stuff out.”

“Whatever.” Ren stood up, putting on his leather jacket. “Just sitting here won’t change anything.”

“Ren, wait, please don’t do something stupid-” Yui reached up to stop him, but before she could,

The door swung open.

Yui gasped. Ren’s hands balled into fists. 

“The new prey.”

Asakura Takeshi stood in the doorway. His voluminous hair framed a bruised and dirty face and sharp eyes that watched Sento with predatory interest. He leaned on the doorframe as he evaluated Sento and Banjou, his snakeskin jacket slouching off one shoulder. The slipping fabric revealed a burn scar that pinched the flesh by his neck tightly.

“Asakura…!” Ren stormed to the door and grabbed a fistful of Asakura’s jacket. 

“I’m not here to play with you, Akiyama.” Asakura pushed him aside roughly. Shinji shot to his feet and stood in front of Yui. His muscles tensed but his eyes betrayed his apprehension.

Banjou rose to his feet too, appraising Asakura warily. Even if he hadn’t been dressed like a serial killer, Asakura’s bloodthirsty eyes elicited a thrum of fear deep inside him. 

To his surprise, Asakura pulled two objects from his jacket’s pocket.

“My advent deck-?” Shinji breathed, then yelped as Asakura threw the card deck at him. He only just caught it to his chest, then stared at it as if it might suddenly disappear.

Asakura similarly threw Sento’s build driver at him. Sento caught it with one hand, gaze not wavering from Asakura.

“A Rider, I assume.” 

“Heh. I don’t care what you use to transform, use it and fight me.” Asakura replied.

* * *

Banjou had warned him about the Mirror World, but Sento wasn’t at all prepared for how this new world felt. Until now, this new place they’d been thrust into had been odd, but familiar. Not like this. 

The air didn’t move. It sat, stagnant, a weight that held everything perfectly still. Every sign was mirrored. Most striking was the cold; even the Build suit couldn’t compensate enough for the chilling bite of this unsettling world. Every so often, a far away, muffled howl pierced the silence. 

Sento, Banjou, Shinji and Ren. Not far from them, leaning against a slender, purple cane, Asakura Takeshi. Violet-tinted metal terminated into spikes on his shoulders, framing a helmet evocative of a cobra. He was watching them. Evaluating them. After a pause, he seemed satisfied, and drew a card from his belt.

“Wait, is that-“ Shinji’s sentence was interrupted. 

_‘Survive vent.’_

Sento wasn’t going to just wait and let Asakura have his way. He pushed himself into a run, fist drawn. Asakura seemed surrounded in shimmering glass. Sento threw his punch-

-and glanced off the glimmering miasma. Asakura was changing, morphing into something new. The glass coalesced like a turbulent lake returning to stillness. His suit was more fearsome now, the cobra hood around his head wider and more menacing. Spikes stuck out from his shoulders, and in his hand was now a long, barbed whip.

“Ouja has a survive card…” Ren muttered. Sento spun on his heel to attack Asakura again. He launched a kick at his chest, connected, drew back. Asakura laughed, unmoved.

“If that’s the best you can do, I don’t want to fight you,” He crowed. 

“Fuck you!” Banjou yelled. He charged at Asakura – only to be easily rebuffed. Again and again he threw himself at the anguiform man, each time thrown asunder as though he were light as a feather. 

Shinji strafed nervously, keeping the same distance between himself and the action. He needed his sword. He drew a card from his deck, slotted it into his Visor.

 _‘Sword vent.’_ He reached up to grasp the sword’s hilt.

_THUMP!_

Shinji yelped as he was thrown aside. He stumbled to the ground, rolling once before struggling back to his feet. 

“Tiger!” 

Kamen Rider Tiger loomed over him. Shinji’s sword stood upright where it had cleaved into the ground, inches from where he now stood. Satoru didn’t give him time to react. Immediately Shinji had to parry a flurry of blows, each one forcing him back a step. Ren ran toward him, sword drawn.

The battlefield split in two. Banjou and Sento struggled against Asakura, gaining no traction against the man’s formidable new suit. Ren and Shinji fared better against Satoru, but Tiger was wearing them out, and fast. 

_‘Strike vent!’_

Tiger slashed Shinji’s chest with its massive claws, sending him flying. Blood dripped from the tips of his claws. The metal glinted in the light. Satoru dug his heel into the ground, muscles tensed. Ready to charge forward and plunge his claws into Shinji’s heart.

“Shinji!”

Claws connected with flesh.

A sharp inhale from shock.

Shinji let out a pained cry.

“Ren!”

Ren keeled over, clutching his stomach. Blood dripped from between his fingers and pooled around him. 

“Don’t get in my way.” Satoru planted his foot on Ren’s shoulder, kicking him aside. Ren gasped, curling onto his side. 

“Stop it! Just stop this!” Shinji pleaded. He staggered to his feet. Satoru eyed him with absent interest.

“I need to kill you, Shinji,” Satoru said matter-of-factly. “Or I can’t become a hero.”

He raised his arm, watching the blood drip from his claws. Then he paused. A flurry of particles rose from his body, as if he were dissipating into the air.

“Out of time,” He said softly. Shinji could feel it too. It was like touching a television just after it was turned off; a soft, fuzzy sensation that spread across his skin. It didn’t hurt at first. But he knew that if they stayed in the Mirror World much longer, it would begin to bite.

He couldn’t bear it any longer. Shinji ran to Ren, frantically trying to get his arm over his shoulder so he could drag his friend to safety.

“Ren, stay awake, okay?” He pleaded. Ren could only groan in response.

Far away from them, Sento watched in rapt curiousity as his hand seemed to begin to blur. Ouja stood some distance away, and swore under his breath.

“Having a time limit is no fun,” He growled. “But I’ll find you two. Don’t keep me waiting for another fight.”

He turned away, sword slung over his shoulder.

“Don’t worry, I’ll be kind. I’ll let you die last.”


End file.
